Radio access coverage provided by cellular mobile networks is usually limited to political boundaries. Along these boundaries the coverage areas overlap. Due to physical irregularities it may happen that at certain areas, coverage is only provided by the network that is operated from the other side of the border.
According to 3GPP standard 3GPP TS 22.011 V9.1.0 (2009-03) 3rd Generation Partnership Project, Technical Specification Group Services and System Aspects, Service accessibility (Release 9), the network selection decision is taken by a user terminal. The user can choose between two standardized network selection methods: manual or automatic network selection. The network selection decision in automatic mode is influenced by results of measurements performed by the user terminal, by various operator provided and user provided network lists indicating preference, equivalence and exclusion and by the capabilities of the mobile terminal. The decision for network selection is taken at the following trigger points, when the mobile terminal is working in automatic network selection mode:                At switch-on or recovery from lack of coverage: according to one option described in TS 22.011 V9.1.0 (2009-03) 3rd Generation Partnership Project, clause 3.2.2.2, the mobile terminal in automatic network selection mode registers itself to the home network, if available.        Periodic network selection interval ends: the interval is a service provider determined value, which is stored on the SIM/USIM. It can range between 6 minutes and 8 hours, with a default of 60 minutes.        If the mobile terminal loses coverage of the registered home network: according to 3GPP TS 25.304 V8.6.0 (2009-06) 3rd Generation Partnership Project, Technical Specification Group Radio Access Network, then the user terminal procedures in idle mode and procedures for cell reselection in connected mode (Release 9), a new network is selected if the mobile terminal is working in automatic network selection mode. Otherwise, the user is prompted to select a different network.        
Further, as long as cells are available that belong to the PLMN that the mobile terminal is currently registered on, no automatic network re-selection is performed. In other words, the mobile terminal will remain registered in the same network as long as possible, except if a network with higher priority has been found at periodic network selection.
With respect to the registration to different networks and related signaling the move of the mobile terminal in idle mode from one radio cell to a neighboring radio cell within the same registration area does not cause any network load and does not cause any problems concerning paging. Registration to a different network requires location registration. Repeated change between registration areas would cause heavy signaling load and increase the risk of a paging message being lost. It is therefore required by 3GPP TS 23.122 V9.0.0 (2009-09) 3rd Generation Partnership Project, Technical Specification Group Core Network and Terminals, Non-Access-Stratum (NAS) functions related to Mobile Station (MS) in idle mode (Release 9), clause 3.3, that the access stratum shall provide a mechanism to limit this effect.
Therefore, it would not be acceptable to implement a mechanism that registers the mobile terminal to the home network HPLMN whenever the home network HPLMN is available. Any proposed solution must be comparable to existing solutions as far as signaling load and location registration frequency is concerned.
Further, in IN 20050195514, Method for GPS based network selection during service origination in multi-rate environment Samsung Electronics Co Ltd. (SMSU), there is proposed a method to select radio access type dependent on GPS determined location of the mobile terminal. The solution requires support by the network and the network decides which RAT shall be used.
Further, in GB 2 395 867, Modifying List of Preferred Networks Stored in SIM in Response to Location Information Orange S.A., France, the list of preferred PLMNs is modified within the mobile terminal based on location information. This allows for additional flexibility concerning network selection preferences, but it does prevent the mobile terminal to register itself to a foreign network while being located in the home country and radio contact to the home network is lost. Neither will it initiate registration back to the home network when radio signal conditions would allow it.
Further, in US 2005/0107109 A1, Network Selection Methods and Apparatus with Home Network Prioritization after Network Signal Recovery or Power-On, John J. Oskorep, preference is given to the home network when contact to the foreign network is lost. It is not prevented that the mobile terminals remains registered to a foreign network when moving within the home country.
Further, in U.S. Pat. No. 7,171,216 B1, Method and System for Detecting a Preferred Wireless Network for a Mobile Device Cisco Technology, Inc., scanning for a micro network is limited to scenarios where the mobile terminal is within the geographical proximity of the micro network. When the preferred network is available, the mobile terminal camps to the preferred network.
However, with the automatic network selection mode users configuring their mobile terminal to perform automatic network selection may experience the following problem when roaming in a region where public land mobile networks PLMN of adjacent countries overlap. When moving within the home country, the mobile terminal may get registered to the foreign network and will remain so until periodic network reselection takes place and the home network is available at that time or until manual intervention by the user.
This behavior is unexpected and unwanted by most users. It may happen unnoticed by the user but can have significant impact on the charging of originating and terminating calls.
With automatic network selection, registration to the foreign network will always happen if radio contact to the home network is lost. Dependent on geographical irregularities it may happen that certain areas are covered by a foreign network but not by the home network.
A common workaround is to choose manual network selection mode when moving within the home country. Users configuring their mobile terminal to work in manual network selection mode will not experience the problems described above when roaming moving the home country.
However, they have to remember to manually select a new network whenever they cross a country border and loose coverage of the network the mobile terminal is registered in. When the user forgets to select the home network upon entering the home country, again the risk exists to originate or terminate calls at different cost than expected.
Further, not selecting a new network when loosing coverage of the current network leads to un-reachability for extended periods of time. For international travelers, manual network selection mode is therefore not the preferred choice, but only for users that usually remain within the home country.